Stability of transparent conducting oxide films deposited by sputtering for solar cells applications

The stability of transparent conducting oxide (TCO) films with bi-layered structures has been tested in air at temperatures up to 550°C. Aluminum-doped ZnO and Sn-doped In₂O₃ (AZO/ITO) transparent conducting oxide (TCO) films were deposited on glass substrates by a home made radio-frequency (RF) magnetron sputtering system at room temperature in pure argon ambient. A typical commercial ITO and AZO films by mid-frequency (MF) magnetron sputtering at a substrate temperature of 350°C were also investigated for comparison. A strong decrease of electrical conductivity was observed after testing at temperature above 350°C for RF deposited bi-layered TCO as well as for the commercial ITO, while the AZO films deposited by MF magnetron sputtering showed a quite stable electrical property at temperature not greater than 500°C. The optical absorption edge was found to shift to the longer wavelength with an increase in testing temperature for all the TCO. MF sputtered AZO films were used as transparent front contacts for the fabrication of copper indium gallium selenide (CIGS) superstrate thin film solar cells.